Silicon carbide hot surface ignitors for the ignition of a vaporous fuel such as natural or artificial gas are well known. Such ignitors are typically employed in gas ovens, ranges, dryers, furnaces, and water heaters and similar appliances.
One example of a hot surface silicon carbide ignitor is disclosed in the U.S. Pat. No. 3,372,305 of Mikulec which is incorporated herein in its entirety by reference. As disclosed therein, the ignitor comprises an elongated hollow body which is made of a non-metallic resistance material such as silicon carbide. The ignitor, which is cylindrical in shape, includes a first portion which includes a pair of laterally spaced elongated members and a second portion comprising a pair of spaced helical bands which are connected to and extend longitudinally from the elongated members. There are two problems associated with the use of such ignitors. The first problem is that silicon carbide ignitors are impact sensitive and therefore require a strong impact resistant metal shield to protect them during shipment, installation and service. Such shields also provide a safety barrier to prevent accidental burns and exposure to possible electrical shock. The second problem is that the metals required for these shields must be quite resistant to the high temperatures generated by the ignitor and the subsequent gas flame. Therefore, the metals fall into the class generally referred to as super alloys.
A further problem is that the super alloy shields are relatively expensive and as such represent a disproportionate portion of the cost of a finished ignitor assembly.
One approach to shielding an ignitor is disclosed in the Schweitzer U.S. Pat. No. 4,029,936 which is also incorporated herein in its entirety by reference. As disclosed therein, an ignitor shield includes a generally box-like structure with a plurality of openings therein. These openings provides sufficient open passages for effective heat transfer from the ignitor to effect ignition of a fuel discharged in the proximity of the ignitor.
A more recent ignitor incorporates a cylindrical shield which is attached to and surrounds the ignitor with a cage-like structure. Such ignitor assemblies have for example been marketed by Surface Ignitors, Inc. the assignee of the present invention. In order to make such ignitor assemblies by the normal manufacturing process, it is necessary to start with a piece or metal, a super alloy which is somewhat wider than the circumference of the part being shielded plus the required stand-off distance. In addition it is necessary to add enough extra metal to provide for a certain amount of overlap.
It is presently believed that an ignitor shield in accordance with the present invention will significantly reduce the amount of super alloy material in an ignitor assembly and enable the production of such assemblies at a significant cost reduction. This cost reduction can be achieved without adversely affecting the durability of the assembly. It is also believed that the shields in accordance with the present invention can be installed in a conventional manner without added complexity or cost for that step of the assembly.